This invention relates to a method of making a liquid filter which includes a roll of filtering material which is fastened in a housing part. The invention relates, more particularly, to a method of making a liquid filter which includes a roll of filtering material which is to be axially traversed by the liquid, which is itself made of a spiral of filtering material wound on a central tube, and which is fastened to a housing part.
In the construction of such filters it has been customary to glue together the outer end face of a spirally wound roll of paper filtering material, rolled up on a central tubular member, to the filtering roll itself. Subsequently, a broad bead of glue material was applied to the outer circumference of the roll, and the roll, prepared in this fashion, was introduced into a cylindrical housing. In practice, excess glue always remained hung up at the edge of the housing and had to be removed either by hand or by special machines. The solidified two-component glue formed a tight, rigid connection between the paper filtering material and the metal housing. This process is difficult to simplify and to automate.
It is further known to make a liquid filter by disposing a zigzag-shaped, folded filter paper web, bent into a ring, between a housing member and a central tube in such a manner that the folded edges of the web formed a bellows running in a star-shaped fashion from the central tube outwardly. The bellows is firstly tightly and rigidly sealed to the housing member, using a thermoplastic foil which lies in the housing member. Only subsequently is the butt of the still-open, central tube sealed. This known construction method uses thermoplastic material and is susceptible to considerable automation of its individual steps, but it can be used only for forming the above-mentioned filter ring roll, having a so-called axial, star-shaped construction. Because of the open tube, filter rolls of this nature can easily be inserted into a housing member.